|
After taking a pressure reading, this measurement should be
corrected for the temperature at which the measurement was recorded.
This adjustment is important because the components of the barometer
(usually mercury, brass, and glass) can expand or contract with
different temperatures.
To make the temperature adjustment, consult the CRC Handbook
of Chemistry and Physics. This book contains a table of observed
height of the mercury column at various temperatures and the
corrections that should be used at these temperatures. Below,
a small portion of the table is excerpted.
Temperature Correction Table
|
Temperature (°C)
|
Observed height in millmeters
|
|
750
|
760
|
770
|
780
|
|
20
|
2.44
|
2.47
|
2.51
|
2.57
|
|
21
|
2.56
|
2.60
|
2.63
|
2.70
|
|
22
|
2.69
|
2.72
|
2.76
|
2.83
|
|
23
|
2.81
|
2.84
|
2.88
|
2.96
|
As an example of how to use the table, imagine that a pressure
reading of 762.3 mmHg was obtained at 22 °C. Using the table,
the correction factor at this temperature and pressure is approximately
2.72 mmHg, since 760 mmHg is the closest value to 762.3 mmHg.
The correction factor is subtracted from the measured value to
obtain a temperature-adjusted reading of 762.3 mmHg - 2.72 mmHg
= 759.6 mmHg.
|
